U.S. patent number 7,155,196 [Application Number 10/150,677] was granted by the patent office on 2006-12-26 for intermediate frequency tuner.
This patent grant is currently assigned to Cypress Semiconductor Corp.. Invention is credited to Paul Beard.
United States Patent |
7,155,196 |
Beard |
December 26, 2006 |
Intermediate frequency tuner
Abstract
The present invention is a method and apparatus for optimizing
performance of a transceiver selecting and processing an
intermediate frequency free of significant interference, such as
noise. A frequency band may be scanned to detect interference upon
which an intermediate frequency free of significant interference
may be selected. This may enhance performance of the receiver by
reducing the effects of noise. Additionally, perrformance may be
further optimized by adjusting the passband of the filter such that
the center of the passband matches the selected intermediate
frequency. This may provide stability as centering of the passband
may account for process, voltage and temperature variations and
errors. Further, performance may be enhanced by ensuring desirable
signal attributes are passed through the filter.
Inventors: |
Beard; Paul (Milpitas, CA) |
Assignee: |
Cypress Semiconductor Corp.
(San Jose, CA)
|
Family
ID: |
37569537 |
Appl.
No.: |
10/150,677 |
Filed: |
May 17, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
60291785 |
May 17, 2001 |
|
|
|
|
Current U.S.
Class: |
455/339;
455/226.2; 455/317; 455/334; 455/296; 455/226.1 |
Current CPC
Class: |
H04B
1/1027 (20130101); H04B 1/28 (20130101) |
Current International
Class: |
H04B
1/16 (20060101) |
Field of
Search: |
;455/339,334,296,317,307,226.1,226.2,226.3,63.1,67.11,67.13,266,340 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Anderson; Matthew
Assistant Examiner: Dao; Minh
Attorney, Agent or Firm: Marger Johnson & McCollom
PC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims the benefit under 35 U.S.C. .sctn.
119 of U.S. Provisional Application Ser. No. 60/291,785 filed on
May 17, 2001. Said U.S. Provisional Application Ser. No. 60/291,785
is hereby incorporated by reference.
Claims
What is claimed is:
1. A method for processing an intermediate frequency signal of a
transceiver, the method comprising: scanning an intermediate
frequency band to measure an interference in the intermediate
frequency band; selecting an intermediate frequency from the
intermediate frequency band, the intermediate frequency selected
based upon a measured interference level at the intermediate
frequency being below a threshold level; and matching a center of a
passband of a filter with the intermediate frequency, wherein an
output of the filter is demodulated to separate a received signal
from a carrier of the intermediate frequency.
2. The method as claimed in claim 1, wherein the intermediate
frequency band is equivalent to an intermediate frequency
strip.
3. The method as claimed in claim 1, wherein the interference is a
change in at least one of amplitude, frequency, and period.
4. The method as claimed in claim 1, wherein the interference is
measured by monitoring a received signal strength indication.
5. The method as claimed in claim 4, wherein scanning the
intermediate frequency band comprises sweeping a local oscillator
of the transceiver.
6. A transceiver comprising: an oscillator, the oscillator
configured to produce an oscillator signal having an output
frequency; a mixer coupled to the oscillator and configured to
accept a received signal and the oscillator signal, the mixer
configured to utilize the oscillator signal to produce a carrier
for the received signal, the carrier having an intermediate
frequency; an adjustable filter coupled to the mixer, the
adjustable filter configured to match a center of a passband of the
adjustable filter to a desired intermediate frequency; and an
interference detector coupled to the oscillator and the adjustable
filter, the interference detector configured to measure an
interference level associated with the oscillator signal, wherein
the desired intermediate frequency is selected based upon the
interference level being below a threshold level.
7. The transceiver as claimed in claim 6, wherein the oscillator is
configured to sweep through a portion of a frequency band.
8. The transceiver as claimed in claim 6, wherein the output
frequency is set at a frequency corresponding to the desired
intermediate frequency and the received signal.
9. The transceiver as claimed in claim 6, wherein the interference
detector includes a received signal strength indicator.
10. The transceiver as claimed in claim 6, wherein the interference
comprises a change in at least one of amplitude, frequency, and
period.
11. An apparatus for processing an intermediate frequency, the
apparatus comprising: means for scanning an intermediate frequency
band to measure an interference in the intermediate frequency band;
and means for selecting an intermediate frequency from the
intermediate frequency band based upon a measured interference in
the intermediate frequency being less than a threshold level, the
selecting means coupled to the scanning means, wherein the
intermediate frequency is demodulated to separate a received signal
from a carrier of the intermediate frequency.
12. The apparatus as claimed in claim 11, further comprising means
for matching a center of a passband of a filter with the
intermediate frequency, the matching means coupled to the selecting
means.
13. The apparatus as claimed in claim 11, wherein the intermediate
frequency band is equivalent to an intermediate frequency
strip.
14. The apparatus as claimed in claim 11, wherein the interference
comprises a change in at least one of amplitude, frequency, and
period.
15. The apparatus as claimed in claim 11, wherein the interference
is measured by monitoring a received signal strength
indication.
16. A method of processing an intermediate frequency, the method
comprising: sweeping an oscillator of a transceiver across an
intermediate frequency band; measuring an interference present in
the intermediate frequency band; selecting an intermediate
frequency from the intermediate frequency band, the intermediate
frequency selected based upon a measured interference at the
intermediate frequency being less than a threshold level; and
matching a center of a passband of a filter to the intermediate
frequency, wherein an output of the filter is demodulated to
separate a received signal from a carrier of the intermediate
frequency.
17. The method as claimed in claim 16, wherein the frequency band
is equivalent to an intermediate frequency strip.
18. The method as claimed in claim 16, wherein the interference
comprises a change in at least one of amplitude, frequency, and
period.
19. The method as claimed in claim 16, wherein the interference is
measured by monitoring a received signal strength indication.
20. The method as claimed in claim 16, wherein selecting the
intermediate frequency occurs in real-time concurrently with the
measuring of the interference.
Description
FIELD OF THE INVENTION
The present invention generally relates to transceivers, and more
particularly to a method and apparatus for improving transceiver
performance by selecting an optimal intermediate frequency signal
of a radiated signal in real-time.
BACKGROUND OF THE INVENTION
Conventional radio receivers typically incorporate an intermediate
frequency (IF) strip. An IF strip allows filtering and
amplification to be performed at a lower frequency and cost than
the radiating frequency. Further, an IF strip is capable of being
set at a frequency above where 1/f noise, direct current, and IP2
offset issues are troublesome.
Intermediate frequency filters known to the art include single
frequency filters and tunable filters. A single frequency tuner
provides stability and selectivity, however, receiver performance
is limited due to a fixed frequency range. Tunable filters provide
flexibility but are subject to stability problems and low
performance. Additionally, while tunable filters may be operable in
some radio-frequency environments, tunable filters do not operate
well in a frequency hopping environment. Consequently, a method and
apparatus for processing an intermediate frequency signal of a
radiated signal that provides enhanced stability and performance
while allowing flexibility is necessary.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method and
apparatus for selecting and processing an intermediate frequency
that may optimize performance of a transceiver. A filter in
accordance with the present invention may be capable of processing
a range of frequencies. Performance may be optimized by adjusting
the passband of the filter such that the center of the passband
matches the selected intermediate frequency.
In a first aspect of the invention, an intermediate frequency free
of significant interference may be selected. In one embodiment of
the invention, a local oscillator (LO) of a transceiver may be
swept and interference may be measured within a range of an
intermediate frequency strip. An intermediate frequency free of
significant interference may be selected on an instantaneous basis.
Utilization of an intermediate frequency free of significant
interference may be advantageous as it may provide for optimal
transceiver performance.
In a second aspect of the invention, upon the selection of an
optimal intermediate frequency, the passband of a filter of the
present invention may be immediately swept to center the passband
of the filter on the selected intermediate frequency. This may
provide stability as centering of the passband may account for
process, voltage and temperature variations and errors. Further,
performance may be enhanced by ensuring desirable signal attributes
are passed through the filter.
It is to be understood that both the forgoing general description
and the following detailed description are exemplary and
explanatory only and are not restrictive of the invention as
claimed. The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate an embodiment of
the invention and together with the general description, serve to
explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The numerous advantages of the present invention may be better
understood by those skilled in the art by reference to the
accompanying figures in which:
FIG. 1 depicts an embodiment of a process for optimizing
transceiver performance in accordance with the present
invention;
FIG. 2 depicts an embodiment of a process of implementing the
process 100 of FIG. 1 in accordance with the present invention;
FIG. 3 depicts an embodiment of a transceiver for implementing
processes 100 and 200 of the present invention; and
FIG. 4 depicts an embodiment of a programmable filter of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made in detail to the presently preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings.
Referring to FIG. 1, an embodiment of a process 100 for optimizing
transceiver performance in accordance with the present invention is
shown. Process 100 may be performed by a transceiver to process an
intermediate frequency portion of a received signal. Process 100
may begin as a transceiver may scan at least a portion of a
frequency band to detect interference 110. A portion of the
frequency band may be equivalent to an intermediate frequency
strip. In one embodiment of the invention, process 100 may be
scanning for the presence of a characteristic, such as a change in
amplitude, frequency or period of a signal. A characteristic may
include noise or other type of interference which may prevent
optimal demodulation of a modulated signal. Upon a scan of at least
a portion of the frequency band, an intermediate frequency is
selected that may be free of significant interference 120. In
accordance with the present invention, transceiver performance may
be improved by utilizing an intermediate frequency that does not
include interference such as noise preventing optimal demodulation
of the desired signal.
Process 100 may continue by matching the center of a passband of an
intermediate frequency filter with the selected intermediate
frequency 230. Matching the center of a passband of an intermediate
frequency filter with the selected frequency may be advantageous as
it may provide further improved performance for a transceiver
implementing process 100 of the present invention. This may provide
stability as centering of the passband may account for process,
voltage and temperature variations and errors. Further, performance
may be enhanced by ensuring desirable signal attributes are passed
through the filter.
Referring now to FIG. 2, an embodiment of a process of implementing
the process 100 of FIG. 1 in accordance with the present invention
is shown. Process 200 may begin by sweeping a local oscillator (LO)
and measuring interference of the swept frequency band. In one
embodiment of the invention, measurement of interference may be
accomplished with a received signal strength indicator (RSSI). The
received signal strength indicator may detect the received signal
strength of the swept frequencies. A frequency with a low received
signal strength indication may be selected as the intermediate
frequency as this particular frequency may be free of significant
interference 220. It should be understood by those with ordinary
skill in the art that other mechanisms for determining a frequency
free of significant interference may be employed in accordance with
the present invention without departing from the scope and spirit
of the present invention.
Upon a selection of a desired intermediate frequency, a local
oscillator may be set to a frequency corresponding with the
selected intermediate frequency and the radiated signal 230. For
example, the local oscillator may be set at a value corresponding
to the sum of the frequency value of the selected intermediate
frequency and the radiated frequency. Additionally, the selected
intermediate frequency information may be transferred to an
intermediate frequency filter of the present invention 240. The
center of the passband of the IF filter may be matched with the
selected intermediate frequency 250.
An advantageous aspect of the present invention is the ability to
perform process 200 in a continuous fashion. Thus, in one
embodiment of the invention, the process of selecting an
intermediate frequency free of significant interference may be
performed in real-time. As a result, the selected intermediate
frequency may account for random noise and random process
variations that may occur as a product is operated in different
environments and operated according to different conditions.
Referring now to FIG. 3, an embodiment of a transceiver 300 for
implementing processes 100 and 200 of the present invention is
shown. In an embodiment of the invention, transceiver 300 may
operate in the 2.4 GHz Industrial, Scientific and Medical (ISM)
band. Additionally, transceiver 300 may operate according to the
BLUETOOTH specification and may be packaged on a single chip.
Transceiver 300 may include an antenna 310 and a pre-selector 320
to aid in the reception of signals. Pre-selector 320 may include a
frequency amplifier and/or filter circuit. Pre-selector 320 may
amplify the desired radiated signal and reduce some of the
off-frequency noise caused by other radiated frequencies. The
received signal may be sent through a mixer 330. A local oscillator
340 may supply an oscillator frequency to mixer 330 in which an
intermediate frequency is produced. In an embodiment of the present
invention, local oscillator 340 is swept and inteference is
measured by interference detector 360.
Interference detector 360 may measure the interference to allow a
selection of an intermediate frequency free of significant
interference. Interference detector 360 may be capable of detecting
a characteristic, such as a change in amplitude, frequency, period,
and the like. In one embodiment of the invention, the
characteristic may be a change in noise. Noise may refer to
unwanted disturbances imposed upon a spread spectrum signal. In one
embodiment of the invention, interference detector 360 may be a
received signal strength indicator (RSSI). The received signal
strength indicator may detect the received signal strength of the
swept frequencies. A frequency with a low received signal strength
indication may be selected as the intermediate frequency as this
particular frequency may be free of significant interference. It
should be understood by those with ordinary skill in the art that
other mechanisms for determining a frequency free of significant
interference may be employed in accordance with the present
invention without departing from the scope and spirit of the
present invention.
IF filter 350 of the present invention may receive the selected
intermediate frequency information from the interference detector
360 of the present invention. In an embodiment of the invention, IF
filter 350 of the present invention may be adjustable. For example,
IF filter 350 of the present invention may match the center of its
passband with the selected intermediate frequency. Demodulator 370
may receive the modulated intermediate frequency carrier. In an
embodiment of the invention, demodulator 370 may separate the
radiated frequency from the intermediate frequency carrier.
Referring to FIG. 4, an embodiment of a programmable filter 400 of
the present invention is shown. In an embodiment of the invention,
programmable filter 400 may be representative of IF filter 350 of
FIG. 3. Programmable filter may receive an input signal 410 and
produce an output signal 420 which has been isolated and amplified.
It should be understood by those with ordinary skill in the art
that the input signal of FIG. 3 may be the intermediate frequency
carrier. Programmable filter 400 may further reduce off-frequency
noise while amplifying the intermediate frequency carrier.
In an embodiment of the invention, programmable filter 400 may
include resistors 440 460, capacitors, and an operational amplifier
430. An advantageous aspect of programmable filter 400 of the
present invention is the ability to tune itself to the selected
intermediate frequency as described in FIGS. 1 3. Adjustment of the
center frequency in an embodiment of the invention may be
controlled by adjusting the resistance of resistor 440. For
example, resistor 440 may be a digitally controlled potentiometer.
A signal relating to the selected intermediate frequency may be
transferred to the potentiometer. This signal may control the
adjust of the resistance of resistor 440 to control the center
frequency of the filter. As a result, the center of the passband
may be adjusted to the selected intermediate frequency.
Additionally, the bandwidth of the passband may be adjustable. The
resistance value of resistors 450, 460 may be adjusted to vary the
bandwidth of the passband of the filter. It should be understood by
those with ordinary skill in the art that other types of
configurations of adjustable filters may be utilized in accordance
with the present invention to match the center of the passband with
a selected intermediate frequency without departing from the scope
and spirit of the present invention.
It is believed that the system and method and system of the present
invention and many of its attendant advantages will be understood
by the forgoing description. It is also believed that it will be
apparent that various changes may be made in the form, construction
and arrangement of the components thereof without departing from
the scope and spirit of the invention or without sacrificing all of
its material advantages. The form herein before described being
merely an explanatory embodiment thereof. It is the intention of
the following claims to encompass and include such changes.
* * * * *